1. Field of the Invention
The present invention relates to an organic electroluminescent device (hereinafter, also referred to as “organic EL device” or “luminescent device”) which can emit light through the conversion of electric energy to light.
2. Description of the Related Art
Recently, research and development on various display devices have been conducted. In particular, organic electroluminescent devices (organic EL devices) have attracted attention because emission can be obtained with high luminance by driving at low voltage.
Further, the application of organic electroluminescent devices to color displays and white light sources have been tried actively. However, it is necessary to improve the characteristics of respective luminescent devices of blue, green, and red in order to obtain high-performance color displays and white light sources.
A red-emission phosphorescent device has been known which uses a platinum porphyrin complex having a cyclic quadridentate ligand as a phosphorescent substance (see, for example, U.S. Pat. No. 6,303,231B1, the disclosure of which is incorporated herein by reference). However, this device has a low maximum emission and there have been needs for the improvement of the device.
Another platinum complex has been reported (for example in U.S. Pat. No. 6,653,654B1, the disclosure of which is incorporated herein by reference) which has a chained bipyridinebased quadridentate ligand or a phenanthroline-based quadridentate ligand. However, this platinum complex is unsatisfactory with respect to the balance between emission characteristics such as color purity and durability. Therefore, there have been needs for improvement thereof.
Further, there have also been needs for the development of organic EL devices which use luminescent substances emitting light of shorter wavelength (i.e., green-emission luminescent substance and blue-emission luminescent substance) and which have improved emission characteristics and durability.